In recent years, electronic devices, such as mobile telephones and personal computers, have spread significantly and available frequency bands of these electronic devices have been increasing. For example, frequencies in several GHz to several tens of GHz bands have been used for mobile telephones, wireless LANs, and so on.
In addition to the increase in frequency, with a reduction in size and thickness of electronic devices and with an increase in performance thereof, functional degradation due to electromagnetic interference in the electronic devices and radiation noise interference to the outside of the devices have been raised as problems. In view of this, the standard of the International Special Committee on Radio Interference (CISPR) regulates 1 to 6 GHz noise.
As a prior art, there is known an electromagnetic wave absorber formed of a composite magnetic body containing a soft magnetic powder, which uses a crystalline material such as Sendust (registered trademark) or silicon steel, and a resin. For example, JP-A-2005-123531 (hereinafter referred to as Patent Document 1) discloses a flat powder which is for use in an electromagnetic wave absorber.
The conventional electromagnetic wave absorber absorbs an electromagnetic wave by the use of a magnetic loss due to an imaginary part magnetic permeability μ″ of the complex magnetic permeability. Therefore, as the imaginary part magnetic permeability μ″ of the complex magnetic permeability corresponding to a using frequency band shows a greater value, the noise suppression effect of the electromagnetic wave absorber is better.
However, there is a problem that the conventional electromagnetic wave absorber has a small imaginary part magnetic permeability μ″ at a GHz-band frequency and thus cannot obtain a sufficient noise suppression effect.